Ultrasonic surgical instrument with integral shaft assembly torque wrench

A surgical instrument, comprising:

• (a) an end effector;
• (b) a shaft assembly having the end effector projecting distally therefrom, wherein the shaft assembly includes an acoustic waveguide extending therethrough and having a proximal end portion configured to rotatably couple with an ultrasonic transducer assembly;
• and
• (c) a torque wrench integrally connected with the shaft assembly and configured to transmit torque applied to the acoustic waveguide up to a predetermined torque, wherein the torque wrench includes:
• (i) a drive disc positioned coaxially with the acoustic waveguide and rotatably secured relative to the shaft assembly such that rotating the shaft assembly simultaneously rotates the drive feature, and
• (ii) a driven disc positioned coaxially with the acoustic waveguide and rotatably secured relative to the acoustic waveguide such that rotating the driven feature simultaneously rotates the acoustic waveguide, and
• wherein the drive disc is engaged with the driven disc to transmit torque from the shaft assembly to the acoustic waveguide up to the predetermined torque, and
• wherein the driven disc is configured to rotatably slip relative to the drive disc upon receiving torque greater than the predetermined torque for limiting coupling of the acoustic waveguide to the ultrasonic transducer assembly to the predetermined torque.

A method for operating a surgical instrument comprising a shaft assembly having an end effector projecting distally therefrom, wherein the shaft assembly includes an acoustic waveguide extending therethrough and a proximal end portion configured to rotatably couple with an ultrasonic transducer assembly, and a torque wrench integrally connected with the shaft assembly and configured to transmit torque applied to the acoustic waveguide up to a predetermined torque, wherein the torque wrench includes a drive disc positioned coaxially with the acoustic waveguide and rotatably secured relative to the shaft assembly such that rotating the shaft assembly simultaneously rotates the drive feature, and a driven disc positioned coaxially with the acoustic waveguide and rotatably secured relative to the acoustic waveguide such that rotating the driven feature simultaneously rotates the acoustic waveguide, the method comprising the steps of:

• (a) rotating the shaft assembly to simultaneously rotate the dive disc, wherein the drive disc is engaged with the driven disc to transmit torque from the shaft assembly to the acoustic waveguide to couple the acoustic waveguide with the ultrasonic transducer assembly until a predetermined torque is reached;
• and
• (b) releasing the driven disc from the drive disc such that the driven disc is configured to rotatably slip relative to the drive disc upon receiving torque greater than the predetermined torque for limiting coupling of the acoustic waveguide to the ultrasonic transducer assembly to the predetermined torque.